The present disclosure relates to an array coil system in which a plurality of loop coils which are arranged in an array are fed with power.
Recently, wireless power transfer systems have been developed to perform non-contact charge of electric vehicles and other devices. Such a wireless power transfer system includes a power transmitting coil provided to a charging apparatus and a power receiving coil provided to an electric vehicle, and uses an electromagnetic induction method, thereby achieving non-contact and efficient power transfer. Since this wireless power transfer system that uses electromagnetic induction transfers a large amount of power, if a metallic foreign body has intruded in the system and is present between the power transmitting coil and the power receiving coil or near these coils, undesired heat may be generated. It is therefore important, for safety, to detect the presence of metal foreign bodies before performing charge.
A method which is in common use to address this problem is as follows: a detector coil for detecting metals is provided and the presence of a metallic object is detected based on change which electromagnetic induction between the metallic object and the detector coil causes in the inductance of the detector coil. According to this method, which is based on the electromagnetic induction, the detector coil is fed with power having a high-frequency component. However, if a plurality of detector coils are arranged above the power transmitting coil, interconnection between the detector coils deteriorates the detection performance.
Therefore, in order to reduce the adverse effect caused by the interconnection between coils, a technique to connect and disconnect the coils to and from a circuit which drives the coils by using switches has been used (see, for example, Japanese Unexamined Patent Publication No. 2004-342040).